The Best Just Got Cheaper
The last year has been just great for CPU reviews. The launch of Nehalem Core i7 last November saw Intel blow everything out of the water by a huge margin. And against all odds, AMD fought back with their surprisingly proficient and aggressively priced Phenom II processors. In fact, AMD still pretty much owns the $200 CPU market, as well as everything below. Until now.
Although the Bloomfield chips (Core i7 9xx series) have been impressive, they were basically retooled server and workstation products moved over to the desktop market segment as a stopgap solution. As such, they required an expensive chipset (X58) and an odd triple-channel DDR3 memory interface. The QPI interface, which connects the CPU to the Northbridge at an incredibly fast 25.6 GB/s, probably accounts for much of the high cost, along with the multiple-socket nature of the chipset’s roots. On X58, the Northbridge itself serves its purpose only as a PCI-E controller, with up to 36 lanes. Everything else was housed on the ICH10 Southbridge – including 6 more PCI-E lanes.
This week, Intel is launching their Lynnfield (Core i7 8xx, Core i5) series of microprocessors. They take everything that makes the original Core i7 so great – and you should read our original Nehalem review if you want a refresher on what that entails – and makes it more suitable for the desktop market. In other words, these new chips are built from the ground-up to be used as desktop CPU’s, not shuffled over from server parts.
The platform on which Lynnfield is built around is not X58 (and the new chips are not compatible with it at all), but P55. Quite a few changes have been made, so let’s take a look:
To directly compare the chipsets, you should open the X58 diagram in a new window.
Basically, Lynnfield completely does away with the “Northbridge” or “IOH”. Instead, they have integrated a PCI-E controller right onto the CPU itself with support of up to 16 lanes. This is enough for dual-graphics configurations, even with an 8x/8x configuration (for now, at least. We’ll have to wait and see what happens with upcoming DX11 GPUs).
Since the PCI-E controller is right on the chip, there is no longer a need for the QPI bus. Instead, the CPU communicates directly with what would have been known as the “Southbridge” (but is now known as a PCH, or Platform Controller Hub) via a 2 GB/s DMI link. That doesn’t sound like much, but remember that the X58 used the exact same bus to communicate between the Northbridge and Southbridge; the 25.6 GB/s QPI was only used to communicate with the PCI-E bus. And now that PCI-E resides on the CPU, there is no need for that link to exist. In fact, the new method may prove to be faster overall, due to lower latencies. So don’t worry about that low number – it is not exactly correct to directly compare it to the QPI.
Also, you’ll notice that Lynnfield drops the triple-channel DDR3 controller in favour of a dual-channel controller. The loss in bandwidth is minimal though, due to the fact that Lynnfield officially runs its memory at 1333 MHz, as opposed to 1066 MHz. Therefore, the theoretical bandwidth difference is only 21.2 GB/s compared to Bloomfield’s 25.5 GB/s. And in the real world, it ends up being even closer.
The new chipset also takes the opportunity to add a couple USB 2.0 ports (14 in total now) and PCI-E lanes (8 in total). The rest is about the same.
While the Lynnfield CPUs carry a significantly reduced TDP (95W compared to 130W), the chip is actually a bit bigger than Bloomfield. While the QPI is gone, the PCI-E that takes it place takes up quite a bit of space. The total die size ends up being 296mm2 (compared to 263) and the transistor count is up to 774 million (compared to 731). You can take a look at Bloomfield’s die here for comparison.